题目

As a rule, domestic servants doing odd jobs are paid ______. A. by the hour     B. by hour C. by an hour     D. by hours 答案：A 解析: by与the连用,可用于表示“以……为标准或单位”。又如：by the week, by the year, by the thousand等。注意：按重量计应表达为by weight。乒乓球掉在地上会弹起来，这是由于    力的作用，它是由乒乓球发生    而产生的．